Portable compact strip chart recorder with lost-motion protective connection to transducer

ABSTRACT

A portable strip chart recorder is provided with a constant speed strip chart advancing drive powered from a clockworks and gear drive unit. The gear drive unit is sealed from the strip chart so that it cannot be tampered with when the strip chart is changed. The constant speed drive comprises a constant speed sprocket spool which engages sprocket holes in a strip chart running between a feed spool and a take-up spool. The feed spool is provided with a drag to allow variations in the rotational speed of the strip chart on the spool and provide tension on the chart whereas the take-up spool is provided with a slip clutch that allows the chart to be wrapped at a constant tangential speed even though the diameter of the chart on the take-up spool varies.

This is a division of application Ser. No. 794,759, filed May 9, 1977,now U.S. Pat. No. 4,141,019.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention pertains to small lightweight waterproof strip chartrecorders that are intended to be carried by hand and located at placeswhere an environmental variable is to be measured for short periods oftime such as 60, 90 or 180 days.

2. Description of the Prior Art

U.S. Pat. No. 3,487,691 illustrates a portable waterproof temperaturerecorder of which this invention is an improvement. In the patentedrecorder the strip chart take-up spool is driven at a constant rpmrequiring that the chart paper have non-linear time graduations tocompensate for changes in the diameter of the chart on the take-upspool. The use of non-linear time graduated paper is undesirable.Secondly, in the patented chart recorder the chart which is removed atfrequent intervals for inspection or replacement was also in acompartment which revealed the drive mechanism. Frequently the drivemechanism was bumped or tampered with inadvertently which made it out ofadjustment causing the subsequently recorded data to be unreliable.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a linear chart drive for alightweight portable recorder of the type shown in U.S. Pat. No.3,487,691.

It is still another object of this invention to provide an improvedlinear strip chart drive for various types of portable strip chartrecorders.

It is another object of this invention to provide a strip chart recorderin which the drive and gear mechanism is separated and isolated from thereplaceable strip chart section to avoid tampering with the drivemechanism.

Basically these objects are obtained by providing a strip chart drivemechanism for a small lightweight recorder which has a sprocket spoolrotated at a constant speed and having a plurality of circumferentiallyequidistantly spaced sprocket teeth. These teeth engage in equidistantlyspaced sprocket teeth engaging holes in a strip chart which is suspendedunder slight tension between a feed spool and a take-up spool. The feedspool has a slight drag producing mechanism which allows the chart paperto be pulled from the spool under slight tension at a constant linearspeed even though the diameter of the chart on the spool will varyduring use. Similarly the take-up spool is provided with a slip clutchwhich will allow the paper to be fed onto the take-up spool at aconstant linear speed even though the diameter of the chart on thetake-up spool will vary during use.

In the preferred embodiment the strip chart recorder includes a casehaving a removable cover with the case having a chart containing enddefined by the cover and a drive end sealed from the chart containingend by an intermediate plate. The intermediate plate must be physicallyremoved by taking out fastening means so that it is difficult for theuser of the chart recorder to get access to the clockworks or the geardrive unit for powering the strip chart.

BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWING

FIG. 1 is a diametrical section of the preferred portable strip chartrecorder embodying the principles of the invention.

FIG. 2 is an exploded view of a clockworks and modular gear drive unitused in the recorder of FIG. 1.

FIG. 3 is a schematic isometric of a strip chart linear drive mechanismemploying the principles of the invention.

FIG. 4 is a fragmentary axial section taken through the feed out take-upspools of the strip chart drive shown in FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

As best shown in FIG. 1 the strip chart recorder includes a case 10having a removable cover 11 which is coupled to the case by a watertight seal 12. Preferably the seal includes an O-ring 13 squeezedbetween flanges 14 which are compressed together by beveled surfaces ona two-piece clamp 16. The sealing mechanism 12 is of conventionalstructure and will not otherwise be described.

The case 10 is provided with a temperature probe 18 that is coupled to astylus 19 by a suitable amplifying mechanism 20 generally of the typeshown in U.S. Pat. No. 3,487,691, the details of which are incorporatedherein by reference thereto. Axial movement of the probe end 21 willprovide pivotal movement of the stylus 19 across the strip chart 22 thatis supported on a platen 24 positioned in the cover 11.

The case is sealed by an intermediate plate 26 with the cover containinga conventional battery powered clockworks 28 and a gear drive unit 30.The gear drive unit is provided with an output gear 32 that drives anintermediate gear 33 which in turn drives a gear 34. The gear 34 isfixed to a shaft which has on its opposite end a pinion gear 36. Thepinion gear meshes with a gear 38 on drive sprocket spool 40. The gear38 also meshes for synchronous rotation with a gear 42 that is on atake-up spool 44. The drive spool is provided with circumferentiallyspaced equidistantly spaced sprocket teeth 46 which engage inequidistantly spaced sprocket teeth engaging holes 48 in the chart 22.The gear 36 drives the sprocket teeth at a continuous rotational speed.The take-up spool is provided with a chart engaging roll 50 that ispushed against the gear 42 by a spring 52 which is wrapped around athreaded shaft 54. A stop washer 56 is threadably mounted on the shaftand can be threaded inwardly and outwardly to change the pressure causedby the spring and thus change the amount of slippage provided on theroll 50. As can be readily seen, by rotating the gear 36 the sprocketteeth 46 will move the strip chart paper at a constant linear speed withchanges in diameter of the chart on the take-up spool being accommodatedby the slip clutch between roll 50 and gear 42.

Strip chart paper is supplied to the sprocket from a feed spool 60having a stationary shaft 66 and a knurled wheel 64. A catch 65 locks arectangular shaft end 62 against rotation. The wheel 64 is rotatablymounted on the stationary shaft 66 which is provided with a spring clip67 and a spring 68. The spring 68 pushes against a washer 70 which isabutted against a boss 72 formed on take-up roll 74. Thus the wheel 64and its roll 74 can be rotated relative to the shaft 66 but only againstthe friction imposed by the washer 70. This friction between the rolland the stationary shaft provides a slight tension or drag on the stripchart as it is being removed from the varying diameter chart on the roll74.

Preferably the axles for rolls 40 and 44 extend out beyond both sides ofa chart holder 80. These axles then snap into slots 82 on a fixed stand84 to secure the chart holder in the container. The slots are formed toaccurately mesh gear 38 with gear 36. Suitable locking screws not shownwill hold and lock the axles in the slots, if desired.

Operation of the chart recorder requires first that the desired driveratio be determined from the gears within the gear drive unit 30 or bythe selection of gears 32,33, and 34. Next the chart holder 80 isremoved and a new chart is slipped onto the feed spool 60. The chart isthen threaded around the drive sprocket and onto the take-up spool. Nextthe chart holder 80 is snapped into the stand so that the gear 38 mesheswith the gear 36. The clockworks is then started and the sprocket spooland take-up spool are driven in synchronism. The diameter of the take-upspool 44 is the same as the diameter of the drive sprocket 46 so thatinitially the take-up spool will rotate its roller 44 at the samerotational speed as the sprocket 40. As the roll of chart paper buildsup on the take-up roll 44, however, the slip clutch will allow the rollto move more slowly rotationally relative to the sprockets so that thestrip chart will not be pulled too tightly by the take-up spool.Similarly the change in diameter of the chart on the feed spool will beaccommodated by the drag mechanism so that the paper can be fed off atthe linear speed.

In order to prevent damage from abnormal over temperature oscillation ofthe stylus or pen arm 19 a release mechanism is provided. The probe end21 is abutted against an abutment 90 on a push rod lever 86 having aslot 88. The linkage 20 includes a center link 89 which rigidly supportsa pin 87. The pin rests in slot 88 and a spring 92, coupled to an ear 94on the link 89, holds the pin against the end of the slot. A weakerspring 97 pulls the pen arm 19 in a clockwise direction.

When the probe end makes an abnormal extension, the pen arm goes offscale and engages the end of slot 96. Further movement of the probe endis then relieved by movement of the slot 88 away from the pin 87. Theaccuracy of the recorder is not effected but costly repairs orrecalibrations from abnormal temperature conditions are eliminated.

While the preferred embodiment of the invention has been illustrated anddescribed it should be apparent that variations will be apparent to oneskilled in the art without departing from the principles herein.Accordingly the invention is not to be limited to the specificembodiment illustrated in the drawing.

The embodiments of the invention in which a particular property orprivilege is claimed are defined as follows:
 1. A portable compact stripchart recorder comprising:a case having a removable cover, a clockworksin said case, a drive unit coupled to said clockworks, a strip chartconnected to said drive unit for transporting the strip chart in a timedmovement, a transducer for measuring an environmental parameter, a penarm movable over and against the strip chart for recording informationon the strip chart, linkage means coupling the pen arm to saidtransducer for correlated movements between the two, means forrestricting off scale movements of the pen arm, said linkage meansincluding release means for allowing movement of the transducer relativeto the pen arm under abnormal measurements whereby the pen arm is notover stressed when restricted against an off scale movement.
 2. Therecorder of claim 1, said release means including a push rod leverengaging the transducer for movement therewith and having a slot, a linkcoupled to the pen arm, pin means on the link and positioned within theslot for conjoint movement therewith, first spring means for holding thepin means against an end of the slot, second spring means for holdingthe pen arm in a direction toward said transducer, and wherein the endof the slot of the push rod lever can move away from the pin means whenthe pen arm movement is resisted to allow relative movement between thetransducer and pen arm.